Cable modem technology is used in a widespread manner throughout the world. In general, the demand for CATV bandwidth and types of signals transmitted on CATV is increasing. Two-way CATV networks have been touted as a promising method of providing communications in cable television systems. However, technical problems have reduced performances of such two-way networks. In particular, interference due to ingress signals has greatly affected the quality of return path (upstream path) communications in two-way networks. Return path communications are communications from the subscribers to the head end facility.
Ingress signals comprise RF noise signals that are generated by sources external to the CATV network and are radiated onto the CATV network through cable faults, terminations, and the like. Some sources of ingress include international short-wave broadcasts; citizens band and ham radio transmissions; television receivers; computers; neon signs, electrical motors, hair dryers, garbage disposals, and other household appliances, and it has been estimated that 95% of ingress signal power originates in subscribers' homes.
Ingress signals are particularly troublesome in the context of return path communications because of the CATV two-way network structural design. In a CATV network, a large number of subscriber generated signals are funneled toward the head end. The ingress signal power on each of the subscriber generated signals is therefore combined and amplified, resulting in a relatively high ingress signal power at the head end facility.
Several approaches known in the art for signal noise reduction in electrical systems are provided herein.
U.S. Pat. No. 5,881,363 describes a method and apparatus for ingress cancellation using a precoding approach at a transmitter combined with filtering at a receiver for improving upstream transmission efficiency.
U.S. Pat. No. 5,881,362 describes a method of reducing noise and ingress in cable return paths by locating blocking filters between the drop cable and home coaxial wiring.
Other prior art references which use filtering means for reducing noise in CATV systems include U.S. Pat. No. 5,937,330, U.S. Pat. No. 6,757,910, U.S. Pat. No. 5,937,330, U.S. Pat. No. 6,321,384, U.S. Pat. No. 4,612,571, and U.S. Pat. No. 6,647,070.
Additional approaches used for reducing noise in CATV systems are disclosed herein.
U.S. Pat. No. 5,881,363 describes a method and apparatus for combating ingress and multi-path in a CATV return channel by using a pre-coder in the transmitter of user equipment and an ingress rejection filter in the receiver of head end equipment.
U.S. Pat. No. 5,199,048 describes a noise canceller for use in a CATV converter which includes a keying pulse processing circuit for removing a noise signal from a keying signal.
U.S. Pat. No. 5,225,902 describes a method for automatically selecting optimum frequencies for transmitting data from remote terminals upstream to a system manager.
U.S. Pat. No. 5,606,725 describes a broadband network with an upstream power transmission level that is dynamically adjusted as a function of the bit error rate.
U.S. Pat. No. 5,742,591 discloses an interference cancellation system for CATV return transmissions. The interference cancellation system reduces the presence of undesirable narrowband interference that corrupts return signal transmissions.
U.S. Pat. No. 5,835,844 describes a gain variance and ingress reduction system which reduces the overall ingress of interferers for an entire CATV system.
US Statutory Invention Registration No. H1858 describes a system intended for use in a cable network which includes a radio frequency (RF) sensing switch for enabling the reverse path when return signals from the remote receiver locations coupled to at least one tap are present and for disabling the reverse path when no return signals from the remote receiver locations coupled to at least one tap are present.
As noted above, various systems and methods are available nowadays for reducing noise in CATV systems. However, these systems and methods are disadvantageous due to their possessing at least one of the following drawbacks: (1) reduction in the level of the returning signal due to inclusions of splitters, filters, and switches, (2) noise compounding from the many subscribers as these systems are intended for use in cable networks (noise reduction may not be as effective as the number of subscribers increases) (3) relatively high cost of fairly complicated systems which provide a limited noise reduction of up to about 70%, and (4) relatively high cost of somewhat complicated microprocessor based systems.
Thus, the system and method of the present invention is advantageous over the above-mentioned systems and methods by achieving a fairly high percentage (approximately 90%) of noise reduction (due to the closeness of the system to the noise point sources, the noise reduction is highly effective), by its relatively low cost, as it is implemented on an existing amplifier and does not require the inclusion of a separate ingress detection unit. Additionally, unlike the above-mentioned systems, the present system does not require technical skill for installation and may be implemented on a home network either by a technician or by the customer himself.